PROJECT SUMMARY Over a third of adults in the United States were previously estimated to have hypertension, defined since 2003 as a blood pressure of 140/90mm Hg. This prevalence is expected to increase throughout the population, but especially among younger adults, given the recent American College of Cardiology (ACC) and American Heart Association (AHA) update to the definition of hypertension to 130/80mm Hg. The ACC/AHA anticipate that the new definition will result in a tripling of prevalence of hypertension in men under 45 and a doubling among women under 45. Therefore, risk factors among young adults are critical to assess. Diet, obesity, and physical activity are known risk factors, and a growing body of evidence suggests that exposures to air pollution are also associated with risk. However, to date, no study has been able to examine the role of multiple environmental exposures throughout childhood on risk of subsequent hypertension in adulthood, nor how environmental exposures interact with features of the built and social environments to influence risk. The objectives of our study are (1) to determine how features of the total environment experienced during childhood are associated with incident hypertension during adulthood; (2) to examine effect modification of the associations of features of the total environment experienced during childhood with incident hypertension; and (3) to explore how known risk factors of hypertension mediate the associations of the total environment on risk of incident hypertension. We will use the unique resources of the Growing Up Today Study (GUTS) to meet these objectives. GUTS is a prospective cohort study of children whose mothers are participants in the ongoing Nurses? Health Study II who were first enrolled when they were 9-15 years of age and are currently 22-38 years of age. We will append information on multiple chemical stressors (particulate matter (PM2.5, PM10, PM2.5-10), NO2, ozone), physical stressors (temperature, humidity, noise, light at night, ultraviolet radiation), features of the built and natural environments (proximity to roadways, greenness, blue space, walkability, population density) to the residential addresses of each participant throughout childhood. We will combine the environmental factors with time-varying data collected on social factors (demographics, family socioeconomic status, family make-up and interactions, relationships, team/club participation, experiences with violence/abuse), mental health scales/symptoms, activities/behaviors (e.g. diet and physical activity), and inherent characteristics (e.g. age, sex/gender, race, age at pubertal development). We expect our findings to provide valuable information on the role of childhood exposures on subsequent disease in adulthood, as well as how exposures to multiple factors interact or mediate these exposures, providing valuable information for individual and population level prevention, future risk assessments, and policy decisions.